Final answer:
The correct phraseology to inform a pilot that they can resume normal speed is "Cancel speed restriction." This lets the pilot adjust the aircraft's speed as needed or according to airspace regulations.
Step-by-step explanation:
The correct phraseology to advise an aircraft when a speed adjustment is no longer needed is "Cancel speed restriction". This informs the pilot that they may resume normal speed operations according to their discretion or as dictated by the regulations of the airspace they are in. Controllers use this phrase to convey that any previously issued speed instructions are no longer in effect, allowing the pilot to make necessary adjustments to the aircraft's speed without waiting for further instructions.